Although the mechanism underlying the relationship between epilepsy and depression is most likely complex and involves other neurotransmitters and neuromodulators [16,18], the results of the present suggest a new strategy for the prevention and reversal of depression in TLE patients through a mechanism involving altered endogenous TRY metabolite ratios via upregulated pro-inflammatory cytokines and IDO expression in certain brain regions. Here, IDO1 is linked to major depressive disorder.